Flagstone set in mortar

Discussion in 'Hardscaping' started by QLC-Texas, Feb 4, 2011.

  1. QLC-Texas

    QLC-Texas LawnSite Member
    Posts: 10

    I am interested in building a flagstone patio to my own house. I have tried to collect as much research as possible and I am getting conflicting advice. My question is this:

    Is it possible to set the flagstone in mortar and have it hold up without pouring a 4" concrete slab under it first?

    I am about 95% sure I want to set it "wet" in mortar instead of using sand or crushed granite to fill in the cracks, unless someone on here can tell me why that would be better.

    Any help would be appreciated. I'm in the landscape maintenance business, but hardscaping is relatively new to me. This is for my house, not a customer's.
  2. integrityman

    integrityman LawnSite Bronze Member
    Posts: 1,713

    Ive never had luck with mortar adhering to flagstone. Seems like it always comes apart.
  3. STL Ponds and Waterfalls

    STL Ponds and Waterfalls LawnSite Bronze Member
    Posts: 1,177

    You can do it but plan on repointing every few years and just a lot more maintenance in general. With you being in TX you might have better luck than I would in my climate. Why are you set against the dry laid method?
  4. QLC-Texas

    QLC-Texas LawnSite Member
    Posts: 10

    It just seems to me that using a mortar underneath and in the gaps would make it more finished and professional looking. Would it be worthwhile to compact a base layer of gravel. then sand or stone dust, then lay the flagstone on that and fill in the gaps with mortar? Also, if I did do a dry flagstone patio, how stable would it be and would it track the sand or crushed granite into my house, ie sticking to my feet, etc.? Thanks for your replies.
  5. FLCthes4:11-12

    FLCthes4:11-12 LawnSite Senior Member
    Posts: 284

    In GA we routinely lay thick flag 1.5" and up on a 4" compacted layer of crusher run. Compact 2" at a time and wet the crusher run as you compact. Then lay the flag on atleast 1" layer of Type S mortar no premix stuff mix it yourself and make it a little stiff. Then I grout with the same. You will have some cracks in the grout line from time to time but as long as the base cant be undermined you will be fine. After doing all that its just as easy to form it up and for a 4" layer of concrete then you can use a thinner flag. Most of the time the cost works out cheaper to use concrete base and thinner flag.
  6. joes169

    joes169 LawnSite Member
    from WI
    Posts: 236

    Very good points, I agree. I did a small area at my own home a few years ago with some extra flag material. If you can live with the cracks and a little maintenance, it can be done. Just keep in mind that parts of Texas are known to have expansive soils. If it was for a customer, I would never do it w/o a stout concrete base.
  7. Joe Cement

    Joe Cement LawnSite Member
    Posts: 30

    We install all stone on a reinforced 4" concrete base. As far as installing the stone we use a portland and typ s mortar mix. Very important to apply a thinset to the stone before u set it. We have never had problems like this. Hope it helps
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